There are many factors and constraints that influence designs of lock and trim assemblies, including the number of lock functions supported, the strength of the lock, the ability of the lock to thwart an attack, and the cost of manufacture. Each design constraint compounds the complexity of such a design, because attempting to accommodate a given design constraint may restrict one's ability to accommodate a different design constraint. Because not all designs are equally effective or practical, and because changing circumstances continually give rise to new design constraints, there is always a need for innovation.
For example, lock and trim assemblies that utilize a door lever commonly engage the spindle directly to the door handle, relying on a stop mechanism to prevent the lever and spindle from rotating. In many such assemblies, it is possible to defeat the stop mechanism by applying a crowbar or long wrench to the lever, shearing off components of the stop mechanism. Therefore, it is advantageous for a lock and trim assembly to be designed in a manner that thwarts such an attack.
As another example, many lock mechanisms require a door handle to be in a neutral, non-latch-retracting position in order to lock the handle. It is therefore advantageous for the trim assembly to incorporate a return spring to bias the handle back to the neutral position and an escapement spring to engage the lock when the handle returns to the neutral position.
Moreover, when choosing a replacement trim assembly for a door, it is important to find a trim assembly that is compatible with the spindle and possibly other elements of the interior latching assembly, that matches the door function (e.g., is it an interior door or an exit door), that is compatible with the handedness of the door, that matches the physical dimensions and relative placement of the mortise and/or bore cylinder, and that matches the physical arrangement of trim mounting holes.
Most trim assemblies, however, are only suitable for a specific type or make of lock. It would be advantageous to have a universal trim assembly that, with minimal substitution or rearrangement of parts, accommodates a wide variety of types and makes of locks, as well as a wide variety of lock functions. However, the design of such an assembly is complicated by the typically tight spacing of trim assembly components. For example, a rearrangement of the trim mounting posts may require a rearrangement of other trim assembly components.
The present invention described below can be characterized in many different ways, not all of which are limited by its capacity to address the above-mentioned issues, needs or design constraints.